The consulate cannot extend/renew the Non-Immigrant O-A (Retirement/Long-Stay Visa) - you will have to re-apply for this type of visa (resubmit all of the required documentation) or you can apply for the extension through Thai Immigration in Thailand.
From: “Order of the Royal Thai Police Headquarters, No. 606/2549, Re: Rules and Conditions in the Consideration of Alien Applications for Temporary Stay in the Kingdom of Thailand”
Consideration for Extending Non-Immigrant O-A (Retirement/Long-Stay) Visa
7.21 In the case of a retiree: Permission will be granted for a period of not more than one year at a time. Qualifications for consideration of extending a Non-Immigrant O-A (Retirement/Long-Stay) Visa include:
(1) The alien has obtained a temporary visa (NON-IM); and
(2) The applicant is 50 years of age or over; and
(3) Proof of income of not less than Baht 65,000 per month; or
(4) Account deposit with a bank in Thailand of not less than Baht 800,000 as shown in bank account transactions for the past 3 months; or
(5) Annual income plus bank account deposit totaling not less than Baht 800,000 as of the filing date of application
(6) For an alien who entered Thailand before October 21, 1998, and continuously allowed to stay in the Kingdom as a retiree, the following shall apply:
(a) He/she must be 60 years of age or over and has regular income. His/her bank account deposit shall not be less than Baht 200,000 a year and evidence of the account deposit for the previous 3 months must be shown; or he/she has a monthly income of not less than Baht 20,000.
(b) If he/she is under 60 years of age but not less than 55, the alien shall have regular income with a bank account deposit of not less than Baht 500,000 a year and evidence of the account deposit for the previous 3 months must be shown, or he/she has a monthly income of not less than Baht 50,000.
Documentation to be submitted includes:
1. Application form
2. Copy of the applicant's passport
3. Proof of income, e.g., retirement pension, interest earnings or dividends, etc.; and/or
4. Certificate of local bank account deposit together with copies of bank account records
5. Only in the case set out in clause (6), the same documentation as stated in clauses 1-4 above shall be required.